Antibodies have been produced in animals that recognize: Melatonin; the N,N-dimethylindolealkylamines (DMT, 5-OH DMT and 5-OCH3 DMT); meperidine (and related congeners substituted on the nitrogen atom of the piperidine group) and normeperidine; 1-alpha-acetylmethadol (LAAM) and its demethylated and deacetylated metabolites; nicotine and its metabolites. Efforts are being continued to obtain antibodies to other pharmacologically active substances of neurochemical interest. These antibodies will be characterized and radioimmunoassays developed to quantify these compounds and their metabolites in biological fluids and tissue extracts, to determine their disposition and to investigate the enzyme systems involved in their metabolism. The ability of antibodies to combine with and neutralize the effects of pharmacologically active substances may permit the neurochemist to use them as specific inhibitors in in vitro and in vivo experiments. While the goal of these studies is to obtain antibodies with strict specificities so that analyses can be carried out directly on physiological fluids and tissue extracts, antibodies that bind closely related compounds are also useful as analytical tools if cross reacting substances are separated by chromatographic means prior to radioimmunoassay.